Since 1954 all automobiles manufactured in the United States of America have been equipped with turn signaling means comprising flashing front and rear turn signal lamps. The turn signal circuit includes a thermal circuit interrupting device, a switching means, and indicating lamps at both sides of the front and rear of the exterior of the vehicle. Some vehicles use the brake and parking lamps for this purpose, and others utilize separate lamps. In either case, the circuit interrupting means operates in series with the lamps which are engaged by the signaling switching means.
The circuit interrupting means generally consists of a thermally operated bimetallic switch which is heated by the current of the signaling lamps to open the series circuit and temporarily extinguish the lamps until the switch cools and reestablishes contact. Thus when the interrupter is in the open circuit mode, the lamps are dark and the full battery voltage is present across the terminals of the interrupter, also known as a turn signal flasher unit. The turn signal flasher unit has become a standardized component for each major automotive manufacturer, generally comprising a cylindrical cannister having spade lug connectors which are received in a standardized plug receptacle within the vehicle.
The switching means for most turn signal systems includes a switch wand on the steering column, and a switch which detects rotation of the steering wheel indicative of a turn having been initiated and completed. Thus cancellation of a turn signal indication is generally accomplished automatically.
The driving public has come to rely on the indication of intent to turn or change lanes which is provided by flashing turn signals. A major problem occurs when the turn signal malfunctions and fails to cancel automatically. For example, the steering wheel rotation required to change lanes often may be insufficient to actuate the cancelling mechanism, and the turn indication may be sustained for many miles of highway driving. Although some turn signal systems generate a clicking sound or other audible indication of operation, this sound is often masked by the noise of highway driving, or vehicular audio entertainment systems, or the like.
A sustained turn signal indication that is erroneous may cause surrounding drivers to take actions which are unnecessary and potentially dangerous. For example, consider two oncoming vehicles approaching an intersection. One vehicle exhibits a right turn signal that is caused by a malfunctioning turn signal system, and the other driver intends to turn left. The driver turning left will assume that the oncoming vehicle is turning right, and that the way is clear to make the left turn. However, the oncoming vehicle travels straight through the intersection, and may collide with the left turning vehicle.
U.S. Pat. No. 4,754,256 discloses a audible turn signalling system which emits a click sound from a loudspeaker with each cycle of the flasher unit. This system, and others like it, operate whenever the turn signal operates, not just when the turn system malfunctions or sustains beyond the turn or lane change.
Clearly there is a need for a warning system which will inform the driver of a vehicle that a turn signal indication has not cancelled following a vehicle turn or lane change. It would be advantageous to retrofit existing vehicle turn signal system with such a warning system, and to provide a warning system that may be retrofit with a minimum of installation labor and wiring.